48 BOTANICAL GAZETTE [july 



different conditions of aeration, drainage, and cropping, is likewise 

 clear. The presence of compounds inimical to plant growth by 

 virtue of a property resembling that of any of the above-mentioned 

 poisons might therefore cause a different fertilizer requirement, a 

 requirement which might even change from time to time according 



biochemical 



remains in the soil: in other 



mana 



ment, and the altered biochemical 



remains 



sim 



The action of fertilizers on soils is a much contested 

 but the weight of evidence is against the assumption 

 effect is due altogether to the added plant food. If so 

 explanation were the true one, nearly a century of investigation 

 of this problem by scientists of all civilized nations would surely 

 have produced greater unanimity of opinion than now exists in 

 regard to fertilization. Thoughtful investigators everywhere 

 are finding that fertilizer salts are influencing many factors which 

 contribute toward plant production besides the direct nutrient 

 factor for the plant. It is this additional influence of fertilizers 

 which makes them doubly effective when rightly used and ineffi- 



>erly used. To this influence of fertilizers on soil 



impro 



due 



on the theory of lacking plant food, and any study which throws 

 further light upon the mooted question is of direct help toward 

 reaching that view of soil fertility and soil fertilization which will 

 eventually result in a more definite system of fertilizer practice, 

 to the end that surer and safer returns are obtained from their use. 

 This will tend to extend fertilizer practice by making it more 

 remunerative and rational than in the past. 



Bureau of Soils 

 U.S. Department of Agriculture 



Washington, D.C. 



